A non-destructive inspection method using X-ray is applied to various areas ranging from industrial use to medical use. An X-ray beam is an electromagnetic wave having a wavelength between approximately 1 pm (10−12 m) to approximately 10 nm (10−8 m). An X-ray beam having a shorter wavelength is referred to as a hard X-ray beam, and an X-ray having a longer wavelength is referred to as soft X-ray beam.
In an absorption contrast method, which uses the difference in transmittance when an X-ray beam transmits a test object, the absorption image acquired in this method exhibits high penetrating power of the X-ray and is put to practical use in internal crack inspection on steel material etc., and security measures, such as baggage inspection.
For a test object that consists of a material having a small density difference, which generates a small contrast due to X-ray absorption, it is effect to use X-ray phase contrast imaging in which a phase shift in the X-ray due to a test object is detected.
As a type of X-ray phase contrast imaging, imaging using an imaging apparatus including a mask that blocks X-ray beams and installed on the edge area of the pixels in the detector unit is disclosed in PTL 1. By setting the apparatus such that an X-ray beam is incident on part of the mask when a test object is not disposed, the positional change of the X-ray due to refraction at the test object can be detected as a change in intensity.
FIGS. 7A and 7B are enlarged views of the detector unit in PTL 1. FIG. 7A is a view of the detector unit in the incident direction of an X-ray beam. FIG. 7B is a view of the detector unit in a direction orthogonal to the incident direction of the X-ray beam.
A shielding element 720 that blocks an X-ray beam is disposed on the edge region of a detection pixel 710 (at the boundary with the adjoin pixel) in the detector unit. An X-ray beam 730 is incident on each pixel such that part of the X-ray beam 730 is incident on the shielding element 720. With such an arrangement, when an X-ray beam is incident on a test object, the position of the incident X-ray beam 730 changes on the detection pixel 710 due to refraction. Since the area of incident X-ray beam blocked by the shielding element 720 changes due to a positional change, the detected intensity of the X-ray beam changes. Therefore, by detecting the changes in the intensity of the X-ray, refraction can be measured.